A binocular type and a multi-ocular type have hitherto been known as a method for displaying naked-eye three-dimensional image. In any of these types, a lenticular sheet, which is a semi-circular lens array having a lens characteristic in only a horizontal direction, or a parallax barrier is provided on a display surface, to thus cause right and left eyes to separately see a two-dimensional image having a parallax error and cause an observer to perceive a stereoscopic image, which is an image which enables perception of a three-dimensional appearance from only one direction. According to a method for displaying three-dimensional image of the binocular type, two two-dimensional images only cause an observer to perceive a three-dimensional image from one direction. However, according to a method for displaying a three-dimensional image of multi-ocular type, four two-dimensional images cause the observer to perceive a three-dimensional image from three directions, for example. Specifically, a motion parallax (a phenomenon by means of which an object appears to move in a direction opposite to a moving direction of a body), although discontinuous, is imparted to an observer.
An II (Integral Imaging) scheme is available as a scheme for rendering a motion parallax more perfect and enabling display of a “Three-dimensional Image (a stereoscopic image having motion parallax).” This scheme is derived from a technique for photographing and reproducing a stereoscopic image called an Integral Photography (IP) scheme proposed in 1908 (see, e.g., Related-art Document 1, which is identified later). This scheme includes: preparing a lens array corresponding to pixels of a steroscopic photograph; performing photography with a film placed at a focal length of the lens array; and placing the lens array used for photography on the photographed film, to thus effect reproduction. As is evident from a process for effecting reproduction by means of reversing only a traveling direction in information about a light beam recorded through a lens, this scheme is an ideal scheme for enabling reproduction of even a perfect aerial image without posing a restriction on the position of an observer as in the case of a holography, so long as the resolution of a film is sufficiently high. In an II-type three-dimensional image display device, a liquid-crystal display (LCD), which is a typical flat panel display, is used in place of a film. Light emitted from pixels passes through a lens, whereby a traveling direction of the light is limited and the light is emitted as a light beam. The greater the number of pixels provided at the rear of the lens; namely, the number of pieces of parallax information (i.e., pieces of image information which are viewed differently according to an angle of view), the wider a display range of the three-dimensional image display device toward the front or back thereof. However, when the resolution of the LCD is constant, a lens pitch becomes longer, so that the resolution of a three-dimensional image is deteriorated (see, e.g., Related-art Document 1).
Particularly, the II (1D-II) scheme for providing parallax information in only a horizontal direction utilizes a lenticular sheet as in the case of the three-dimensional image display method of multi-ocular type, and classification of the II scheme is likely to be confused. However, a characteristic of the II scheme lies in that the number of parallax errors is increased within a practicable range in consideration of a decrease in the resolution of a viewpoint image and that the position of an observer is not presumed at the time of designing of a light beam (i.e., a light collection point is not provided for each of the eyes at the time of observation). These characteristics conclusively differ from the design of the three-dimensional image display method of multi-ocular type that is characterized in that the number of parallax errors is reduced to a low value of 2 to 4 in order to prevent occurrence of a decrease in the resolution of a view point image and that light collection points are provided at positions corresponding to the eyes, to thus cause the eyes to perceive a stereoscopic image. Specifically, a horizontal lens pitch or an integral multiple thereof is designed to be an integral multiple of a horizontal pixel pitch, to thus cause beams exiting from a plurality of lenses to go out so as to become essentially parallel to each other. Thus, occurrence of, in a reproduction-observation space, a special point at which beams are concentrated is prevented (a method for setting light collection points sufficiently rearward of an observation distance is also available). In relation to these beams, though discretely light from a surface—which is acquired when a substance is actually present—is extracted and reproduced. Therefore, by means of increasing the number of parallax errors to a certain extent, the observer can visually ascertain, within an observation range, a binocular viewpoint image to be substantially viewed from the position of the observer, and consecutive parallax errors can be obtained. Through close examination, a difference between the II type and the multi-ocular type finally is determined to be a difference in arrangement of beams to be limited because the number of pixels of the flat panel typified by an LCD is finite. However, when compared with the three-dimensional image display method of multi-ocular type in which a motion parallax is incomplete as a result of an emphasis being placed on the resolution of a viewpoint image, the beam design of the 1D-II scheme that does not provide a special light collection point enables realization of a more natural three-dimensional image which lessens fatigue and takes into consideration a balance between a binocular parallax and a motion parallax (see, e.g., Related-art Document 2, which is identified later).
Thus, the 3-D display includes various schemes. Of these schemes, the II scheme is a superior 3-D display scheme that produces a more natural, fatigueless three-dimensional image.
However, the II scheme requires generation of a stereoscopic image by use of images captured when a target to be expressed stereoscopically is viewed from an extremely large number of viewpoints. Particularly, in the case of a CG image, a stereoscopic image must be generated by use of a plurality of images rendered from an extremely large number of viewpoints (see, e.g., Related-art Document 2).
In order to implement this processing operation through use of ordinary CG rendering operation, rendering operation must be repeatedly performed, from each of viewpoints, by an amount equal to the number of viewpoints.
An image format called a tile image format has already been conceived as a format for efficiently storing CG rendering images generated from a plurality of viewpoints. In order to convert a group of CG rendering images captured from a plurality of viewpoints into a tile image format, processing which is not presumed much in ordinary CG processing must be used frequently.
Related-art Document 1: M. G. Lippmann, Comptes Rendusde l'Académie des Sciences, Vol. 146, pp. 446 to 451 (1908).
Related-art Document 2: T. Saishu, et al., “Distortion Control in a One-Dimensional Integral Imaging Autostereoscopic Display System with Parallel Optical Beam Groups,” SID 04 Digest, pp. 1438-1441, 2004.
As mentioned above, in order to produce a CG image for use with a 3-D display; especially a CD image for a II scheme, there are required (1) CG rendering operation from many viewpoints and (2) shaping of rendering images in a predetermined format (e.g., a tile image format for the case of the II scheme).
In relation to (1), in the case of, e.g., the II scheme, rendering from many viewpoints—ordinary 20 viewpoint or more—is usually required. Iteration of rendering operation involves consumption of a corresponding time, thereby posing a problem of a time to generate CG image becoming extremely long.
In relation to (2), a group of rendering images must be shaped in a predetermined format (e.g., a tile image). However, in order to perform shaping efficiently, rendering operation must be performed in the manner of usage which is not presumed much in ordinary CG. General-purpose graphics processing hardware (GPU: Graphics Processing Unit) is designed to exhibit extremely high performance within a presumed range. Therefore, when being used in excess of the presumed use method, the GPU fails to exhibit sufficient performance, which in turn raises a problem of deterioration of rendering speed.
In order to solve the problem, custom-designed graphics processing hardware—which is specialized for generating a CG image for use with a 3-D display and can exhibit best performance when used in such a way—must be developed. However, use of custom-designed hardware poses difficulty in providing inexpensive generation of a CG image for use with a 3-D display.